The electric length of cable

   The parameter that often calls electric length with in transmission line (unit: MHZ) the electric function that will measure cable. When the factory produces cable, because of the relation of workmanship, make the electric index of each batches cable is existing difference, it is two cable like length of a paragraph of physics together for instance, right same an electric performance that it reflects for high frequency signal is different, because this introduced the idea of length of a report. It was mirrorred inside length of physics of a paragraph of unit, cable shows the character that come to place of some frequency signal. In the feed system that makes emissive antenna, this parameter is attached most importance to especially should. Publish in me for example " of double deck cross emissive antenna deserve to receive " the cable of each minutes of feed in one article, it is like physical length but below the situation with electric different length, the actual impedance of the line that divide make a present of can produce deflection and can cause add phase shift, make whole antenna system is accomplished hard deserve very well to receive.
   So how to go detecting the electric length of a paragraph of cable? Specific means is such, the central frequency that emits aerial job for example is F, its corresponding wavelengh is λ , length of a physics is intercept λ / the cable of 2 the terminal short circuit it, make it forms total reflection to signal, have a test with sweep generator, adjust the weaveform that the central frequency that sweep generator outputs makes a cave in arises on sweep generator screen (place of the L that be like a graph is shown) , wave of this cave in is the reflection weaveform of cable. From long term we know in theory, the transmission line of terminal short circuit to some frequency signal, from terminal λ / 2 place, amplitude of its reflection wave electric current is the biggest, the A in pursueing right now so is nodded (namely the frequency of correspondence of wave crest location) the electric length that is this cable. If A nods the frequency that the frequency mark of place indicates to be equal to F, the electric performance that shows this cable amounts to mark, if differ F, the electric performance that shows cable is existing difference, when the line dividing make a present of that if use this cable,makes aerial system, must want to be opposite its (physical length) undertake correction.
   To characteristic and identical cable, when its physical length is identical, their electric length is identical also; When its character differs, the physical length of cable is identical and their electric length is not identical, so we can use electric length the consistency that this index will arrive measure cable performance.

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